Decentralized electrical power allocation system

ABSTRACT

A decentralized electrical power allocation system is provided. The system includes a power bus, electric power consumers, and at least two power source assemblies. Each power source assembly includes a power controller and a power source. Each power controller is configured to execute an adaptive droop control scheme so as to cause their respective power sources to output power to meet a power demand on the power bus applied by the power consumers. The power output of a given power source is controlled based at least in part on correlating a power feedback of the given power source with a droop function that represents an efficiency of the given power source to generate electrical power for a given power output. The droop functions are collaboratively defined so that one power source shares more output at lower power levels while another power source shares more output at higher power levels.

FIELD

The present disclosure relates to electrical power systems for vehicles,such as aircraft.

BACKGROUND

Aircraft and other vehicles can include electrical power systems thatinclude power sources that provide electric power to power consumers.Conventionally, a centralized approach has been taken to allocate thepower output from each power source to meet the power demand of thepower consumers. For instance, supervisor controllers have been used todetermine the load share that each power source is responsible to outputin order to meet the power demand of the power consumers. Suchconventional systems may have certain drawbacks.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present disclosure, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 is a schematic top view of an aircraft in accordance with anexample embodiment of the present disclosure;

FIG. 2 is a schematic, cross-sectional view of a gas turbine engine ofthe aircraft of FIG. 1 ;

FIG. 3 provides a schematic perspective view of a fuel cell assembly ofthe aircraft of FIG. 1 ;

FIG. 4 provides a close-up, schematic view of one fuel cell of the fuelcell assembly of FIG. 3 ;

FIG. 5 provides a system diagram of an electrical power system accordingto an example embodiment of the present disclosure, the electrical powersystem having a direct current power bus;

FIG. 6 provides a logic flow diagram for allocating power to be outputby a first power source of the electrical power system of FIG. 5 ;

FIG. 7 provides a logic flow diagram for allocating power to be outputby a second power source of the electrical power system of FIG. 5 ;

FIG. 8 provides a graph depicting a first droop function associated withthe first power source overlaid with a second droop function associatedwith the second power source of the electrical power system of FIG. 5 ;

FIG. 9 provides a graph representing a non-linear first droop functionassociated with the first power source overlaid with the second droopfunction associated with the second power source on a DC bus voltageversus power output graph;

FIG. 10 provides a system diagram of another electrical power systemaccording to an example embodiment of the present disclosure, theelectrical power system having an alternating current power bus;

FIG. 11 provides a logic flow diagram for allocating power to be outputby a first power source of the electrical power system of FIG. 10 ;

FIG. 12 provides a logic flow diagram for allocating power to be outputby a second power source of the electrical power system of FIG. 10 ;

FIG. 13 provides a graph representing the first droop functionassociated with the first power source overlaid with the second droopfunction associated with the second power source on an AC bus frequencyversus power output graph;

FIG. 14 provides a graph depicting a first droop function associatedwith a first power source overlaid with a second droop functionassociated with a second power source of an electrical power system;

FIG. 15 provides a graph depicting a first droop function associatedwith a first power source overlaid with a second droop functionassociated with a second power source of an electrical power system;

FIG. 16 is a flow diagram of a method of operating a decentralized powerallocation system for an aircraft in accordance with an example aspectof the present disclosure; and

FIG. 17 provides a computing system according to example embodiments ofthe present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to present embodiments of thedisclosure, one or more examples of which are illustrated in theaccompanying drawings. The detailed description uses numerical andletter designations to refer to features in the drawings. Like orsimilar designations in the drawings and description have been used torefer to like or similar parts of the disclosure.

The singular forms “a”, “an”, and “the” include plural references unlessthe context clearly dictates otherwise.

The terms “upstream” and “downstream” refer to the relative directionwith respect to fluid flow in a fluid pathway. For example, “upstream”refers to the direction from which the fluid flows, and “downstream”refers to the direction to which the fluid flows.

The present disclosure relates to electrical power systems for vehicles,such as aircraft. Such electrical power systems can include powersources that provide electrical power to one or more power consumers.Conventionally, centralized power allocation systems have beenimplemented to allocate the power output from each power source to meetthe power demand of the power consumers. Such conventional powerallocation systems typically employ a supervisor controller thatdetermines the load share that each power source is responsible tooutput in order to meet the power demand. Such conventional centralizedsystems may have certain drawbacks. For instance, the supervisorcontroller may act as a single point of failure, robust communicationnetworks are typically needed, and scaling the electrical power systemwith a greater number of power sources and/or power consumers can bechallenging.

Accordingly, in accordance with the inventive aspects of the presentdisclosure, various embodiments of decentralized electrical powerallocation systems are provided. The decentralized electrical powerallocation systems provided herein address the drawbacks of conventionalcentralized power allocation systems and offer collaborative andadaptive control of the power outputs of the power sources to meet apower demand on a power bus applied by the one or more power consumers.Particularly, the power sources are each controlled by their respectivepower controllers according to an adaptive droop control scheme thatleverages an efficiency of the power sources to generate electricalpower for a given power output. Each power controller executes adaptivedroop control logic in which power feedback associated with a givenpower source is correlated to a droop function to ultimately determinethe power output or load share of the given power source to meet thepower demand. The adaptive droop control scheme implemented by thedecentralized electrical power system is collaborative in that the droopfunctions are predefined to optimize the efficiency of the power sourcesto meet the power demand. The adaptive droop control scheme is adaptivein that the droop functions can be selected from a plurality of droopfunctions based on, e.g., operating conditions of the vehicle, thehealth or degradation of components of the electrical power systemand/or vehicle generally, etc. In this regard, the droop functions canbe selected for correlation purposes based on the unique operatingconditions or health status associated with the vehicle or componentsthereof.

In one example aspect, a decentralized power allocation system for anaircraft is provided. The decentralized power allocation system includesa power bus, such as a direct current power bus (DC power bus) or analternating current power bus (AC power bus). The decentralized powerallocation system also includes one or more electric power consumerselectrically coupled with the power bus. Further, the decentralizedpower allocation system includes at least two power source assemblies,including a first power source assembly and a second power sourceassembly. The first power source assembly has a fuel cell electricallycoupled with the power bus and a first power controller having firstpower electronics and one or more processors configured to executeadaptive droop control logic so as to cause the first power electronicsto control a power output of the fuel cell based at least in part on afirst droop function that represents an efficiency of the fuel cell togenerate electrical power for a given power output of the fuel cell. Thesecond power source assembly has an electric machine electricallycoupled with the power bus. The electric machine is mechanically coupledwith a gas turbine engine, such as a turbofan engine. The second powersource assembly also includes a second power controller having secondpower electronics and one or more processors configured to executeadaptive droop control logic so as to cause the second power electronicsto control a power output of the electric machine based at least in parton a second droop function that represents an efficiency of the electricmachine to generate electrical power for a given power output of theelectric machine.

The first droop function and the second droop function arecollaboratively defined such that they intersect at a pointcorresponding to a reference power level and are coordinated so that thepower output of the fuel cell is greater than the power output of theelectric machine at power levels less than the reference power level andso that the power output of the electric machine is greater than thepower output of the fuel cell at power levels greater than the referencepower level. Accordingly, when relatively low power is needed, such asduring ground idle or taxi operations of an aircraft, the adaptive droopcontrol scheme allows for the fuel cell to handle all or a majority ofrelatively low power demand on the power bus. This takes advantage ofthe physics and characteristics of the fuel cell to operate at highefficiency at low power levels whilst also saving fuel and wear on theelectric machine and gas turbine engine to which the electric machine iscoupled. Moreover, when relatively high power is needed, such as duringflight operations of an aircraft, the adaptive droop control schemeallows for the electric machine mechanically coupled with the gasturbine engine to handle a majority of the relatively high power demandon the power bus. This takes advantage of the physics andcharacteristics of the electric machine to operate at high efficiency athigh power levels whilst also using the fuel cell in part to meet thepower demand on the power bus.

Referring now to the drawings, wherein identical numerals indicate thesame elements throughout the figures, FIG. 1 provides a schematic topview of an aircraft 10 as may incorporate various embodiments of thepresent disclosure. As shown in FIG. 1 , the aircraft 10 defines alongitudinal direction L and a transverse direction T. The aircraft 10also defines a longitudinal centerline 12 that extends therethroughalong the longitudinal direction L. The aircraft 10 extends between aforward end 14 and an aft end 16 along the longitudinal direction L.

In addition, the aircraft 10 includes a fuselage 20 and a pair of wings22, including a first wing 22A and a second wing 22B. The first wing 22Aextends outward from the fuselage 20 generally along the transversedirection T, from a port side 24 of the fuselage 20. The second wing 22Bsimilarly extends outward from the fuselage 20 generally along thetransverse direction T from a starboard side 26 of the fuselage 20. Theaircraft 10 further includes a vertical stabilizer 32 and a pair ofhorizontal stabilizers 36. The fuselage 20, wings 22, and stabilizers32, 36 may together be referred to as a body of the aircraft 10.

The aircraft 10 of FIG. 1 also includes a propulsion system. Thepropulsion system depicted includes a plurality of aircraft engines, atleast one of which is mounted to each of the pair of wings 22A, 22B.Specifically, the plurality of aircraft engines includes a firstaircraft engine 44 mounted to the first wing 22A and a second aircraftengine 46 mounted to the second wing 22B. In at least certainembodiments, the aircraft engines 44, 46 may be configured as turbofanengines suspended beneath the wings 22A, 22B in an under-wingconfiguration. Alternatively, in other example embodiments, the aircraftengines 44, 46 may be mounted in other locations, such as to thefuselage 20 aft of the wings 22. In yet other embodiments, the firstand/or second aircraft engines 44, 46 may alternatively be configured asturbojet engines, turboshaft engines, turboprop engines, etc. Further,in other embodiments, the aircraft 10 can have less or more than twoaircraft engines. The aircraft 10 can include one or more upper levelcomputing devices 40 communicatively coupled with engine controllers ofthe first and second aircraft engines 44, 46 so as to command a thrustoutput of the first and second aircraft engines 44, 46. The upper levelcomputing devices 40 may receive various sensor inputs that may indicatethe operating conditions associated with the aircraft 10, such as theflight phase, altitude, attitude, weather conditions, weight of theaircraft 10, etc. The upper level computing devices 40 can becommunicatively coupled via a communication network with variousprocessing devices onboard the aircraft 10, such as processorsassociated with power controllers.

As further shown in FIG. 1 , the aircraft 10 includes an electricalpower system 50. For this embodiment, the electrical power system 50includes a power bus 52 to which a plurality of electric power sourcesand a plurality of electric power consumers are electrically coupled.Particularly, for the depicted embodiment of FIG. 1 , the electricalpower system 50 includes a first electric machine 54 mechanicallycoupled with the first aircraft engine 44 (e.g., to a shaft thereof), asecond electric machine 56 mechanically coupled with the second aircraftengine 46 (e.g., to a shaft thereof), and an electric energy storagesystem 58 having one or more batteries, capacitors, etc.

FIG. 2 provides a schematic, cross-sectional view of the first aircraftengine 44 and depicts the first electric machine 54 mechanically coupledthereto. As shown in FIG. 2 , the first aircraft engine 44 defines anaxial direction A1 (extending parallel to a longitudinal centerline 101provided for reference), a radial direction R1, and a circumferentialdirection (extending about the axial direction A1; not depicted in FIG.2 ). The first aircraft engine 44 includes a fan section 102 and a coreturbine engine 104 disposed downstream of the fan section 102.

The core turbine engine 104 includes an engine cowl 106 that defines anannular core inlet 108. The engine cowl 106 encases, in a serial flowrelationship, a compressor section including a booster or low pressure(LP) compressor 110 and a high pressure (HP) compressor 112; acombustion section 114; a turbine section including a high pressure (HP)turbine 116 and a low pressure (LP) turbine 118; and a jet exhaustnozzle section 120. The compressor section, combustion section 114,turbine section, and jet exhaust nozzle section 120 together define acore air flowpath 121 extending from the annular core inlet 108 throughthe LP compressor 110, HP compressor 112, combustion section 114, HPturbine 116, LP turbine 118, and jet exhaust nozzle section 120. A highpressure (HP) shaft 122 drivingly connects the HP turbine 116 to the HPcompressor 112. The HP shaft 122 and rotating components of the HPcompressor 112 and the HP turbine 116 that are mechanically coupled withthe HP shaft 122 collectively form a high pressure spool 160. A lowpressure (LP) shaft 124 drivingly connects the LP turbine 118 to the LPcompressor 110. The LP shaft 124 and rotating components of the LPcompressor 110 and the LP turbine 118 that are mechanically coupled withthe LP shaft 124 collectively form a low pressure spool 180.

The fan section 102 may include a fixed or variable pitch fan 126 havinga plurality of fan blades 128 coupled to a disk 130 in a spaced apartmanner. As depicted, the fan blades 128 extend outward from the disk 130generally along the radial direction R1. For the variable pitch fan 126of FIG. 2 , each fan blade 128 is rotatable relative to the disk 130about a pitch axis P_(X) by virtue of the fan blades 128 beingmechanically coupled to an actuation member 132 configured tocollectively vary the pitch of the fan blades 128 in unison. The fanblades 128, disk 130, and actuation member 132 are together rotatableabout the longitudinal centerline 12 by the LP spool 180. As notedabove, in some embodiments, the fan blades 128 may be fixed and notrotatable about their respective pitch axes. Further, in otherembodiments, the LP spool 180 may be mechanically coupled with the fan126 via a gearbox.

Referring still to FIG. 2 , the disk 130 is covered by a spinner orrotatable front hub 136 aerodynamically contoured to promote an airflowthrough the plurality of fan blades 128. Additionally, the fan section102 includes an outer nacelle 138 that circumferentially surrounds thefan 126 and/or at least a portion of the core turbine engine 104. Thenacelle 138 is supported relative to the core turbine engine 104 by aplurality of circumferentially-spaced outlet guide vanes 140. Adownstream section 142 of the nacelle 138 extends over an outer portionof the core turbine engine 104 so as to define a bypass passage 144therebetween.

In addition, for this embodiment, the first electric machine 54 ismechanically coupled with the LP spool 180. Particularly, the firstelectric machine 54 is directly mechanically coupled to the LP shaft124. In other embodiments, the first electric machine 54 can beindirectly mechanically coupled to the LP shaft 124, e.g., via agearbox. In yet other embodiments, the first electric machine 54 can bedirectly or indirectly mechanically coupled to the HP spool 160, such asdirectly to the HP shaft 122 or indirectly with the HP shaft 122 by wayof a gearbox. In further embodiments, where the first aircraft engine 44has a low pressure spool, an intermediary pressure spool, and a highpressure spool, the first electric machine 54 can be directly orindirectly mechanically coupled to the intermediary spool, such asdirectly or indirectly to an intermediary shaft of the intermediaryspool.

The first electric machine 54 includes a rotor 54A and a stator 54B. Therotor 54A is rotatable with the LP shaft 124. The stator 54B includeselectric current-carrying elements, such as windings or coils. In thismanner, electrical power can be transmitted to or from the electriccurrent-carrying elements, and as will be appreciated, electrical energycan be converted into mechanical energy in a motoring mode or mechanicalenergy can be converted into electrical energy in a generating mode asthe rotor 54A rotates relative to the stator 54B. The rotor 54A hasrotor components for creating a rotor magnetic field in order to coupleto the stator magnetic field to enable energy conversion. The rotorcomponents of the rotor 54A can be, without limitation, rotor magnets incase of a permanent magnet synchronous machine, a squirrel cage in caseof an induction machine, or a field winding in case of a field woundsynchronous machine.

It should also be appreciated that the first aircraft engine 44 depictedin FIG. 2 and the first electric machine 54 mechanically coupled theretoare provided for example purposes and are not intended to be limiting.In other embodiments, the first aircraft engine 44 may have otherconfigurations. For example, in other embodiments, the first aircraftengine 44 may be configured as a turboprop engine, a turbojet engine, adifferently configured turbofan engine, or an unducted turbofan engine(e.g., without the nacelle 138, but including the stationary outletguide vanes 140). For example, the gas turbine engine may be a gearedgas turbine engine (e.g., having a reduction gearbox between the LPshaft 124 and fan 126), may have any other suitable number orconfiguration of shafts/spools (e.g., may include an intermediate speedshaft/turbine/compressor), etc. Furthermore, it will be appreciated thatthe second electric machine 56 can be configured and mechanicallycoupled with the second aircraft engine 46 (FIG. 1 ) in a same orsimilar manner as the first electric machine 54 is configured andmechanically coupled with the first aircraft engine 44.

Returning now to FIG. 1 , the first electric machine 54, the secondelectric machine 56, and the electric energy storage system 58 can eachact as electric power sources, or in some instances, as electric powerconsumers. For example, in some instance, the first electric machine 54and/or the second electric machine 56 can be electric generatorsconfigured to be driven by their respective first and second aircraftengines 44, 46 to generate electric power that can be supplied to one ormore electric power consumers. In other instances, the first electricmachine 54 and/or the second electric machine 56 can be electric motorsconfigured to drive their respective aircraft engines 44, 46, e.g., in apower assist operation. Accordingly, in such instances, the propulsionsystem can be a hybrid-electric propulsion system. In some embodiments,the first and/or second electric machines 54, 56 can be combinationmotor/generators controllable in a generator mode or motor mode. Theelectric energy storage system 58 can be controlled to either provideelectric power to one or more electric power consumers or draw electricpower, e.g., for charging. The electrical power system 50 also includesa plurality of electric loads 70 that consume but do not produceelectric power, such as an aircraft air conditioning system, avionicscomputing devices, aircraft control systems, cabin lights, etc.

As further depicted in FIG. 1 , the electrical power system 50 alsoincludes a fuel cell assembly 60 that is a component of an environmentalcontrol system assembly 62 (or “ECS assembly 62”). The fuel cellassembly 60 can provide electrical power to the plurality of electricloads 70 and/or to the first electric machine 54, the second electricmachine 56, and/or to the electric energy storage system 58 depending ontheir configurations or mode of operation. The ECS assembly 62 islocated generally at a juncture between the first wing 22A and thefuselage 20. However, in other exemplary embodiments, the ECS assembly62 may additionally or alternatively be located at other locationswithin the aircraft 10, such as at a juncture between the second wing22B and the fuselage 20, at the aft end 16 of the aircraft 10, etc. Insome embodiments, the ECS assembly 62 can include more than one fuelcell assembly, such as two fuel cell assemblies.

FIG. 3 provides a schematic perspective view of the fuel cell assembly60 of FIG. 1 . The fuel cell assembly 60 includes a fuel cell stack 64.The fuel cell stack 64 includes a housing 65 having an outlet side 66and a side that is opposite to the outlet side 66, a fuel and air inletside 67 and a side that is opposite to the fuel and air inlet side 67.The fuel cell stack 64 can include a plurality of fuel cells 68 that are“stacked,” e.g., side-by-side from one end of the fuel cell stack 64(e.g., fuel and air inlet side 67) to another end of the fuel cell stack64 (e.g., side 69). As such, the outlet side 66 includes a plurality ofoutlets 80, each from a respective fuel cell 68 of the fuel cell stack64. During operation, output products 82 are directed from the outlets80 out of the housing 65. In some embodiments, the outlets 80 caninclude separate fuel outlets (which may be in fluid communication with,e.g., a fuel exhaust line) and air outlets (which may be in fluidcommunication with e.g., a fuel cell outlet line of a cabin exhaustdelivery system). The fuel and air inlet side 67 includes one or morefuel inlets 84 and one or more air inlets 86. Optionally, one or more ofthe inlets 84, 86 can be on another side of the housing 65. Each of theone or more fuel inlets 84 can be fluidly coupled with, e.g., a fueldelivery line of a fuel delivery system. Each of the one or more airinlets 86 can be fluidly coupled with, e.g., a fuel cell inlet line ofan air delivery system.

FIG. 4 provides a close-up, schematic view of one fuel cell 68 of thefuel cell stack 64 of FIG. 3 . The fuel cells 68 of the fuel cellassembly 60 are electro-chemical devices that may convert chemicalenergy from a fuel into electrical energy through an electro-chemicalreaction of the fuel, such as hydrogen, with an oxidizer, such as oxygencontained in the atmospheric air. Accordingly, the fuel cell assembly 60can advantageously be utilized as a power source. The example fuel cell68 depicted in FIG. 4 , and each of the fuel cells 68 of the fuel cellstack 64 of FIG. 3 , are configured as proton exchange membrane fuelcells (“PEM fuel cells”), also known as a polymer electrolyte membranefuel cell. PEM fuel cells have an operating temperature range andoperating temperature pressure determined to work well with theconditions associated with aircraft and other vehicles.

As depicted schematically in FIG. 4 , the fuel cell 68 includes acathode side 88, an anode side 90, and an electrolyte layer 92positioned between the cathode side 88 and the anode side 90. Thecathode side 88 can include a cathode 89 and the anode side 90 caninclude an anode 91. Further, the cathode side 88 includes a cathodeinlet 93 and a cathode outlet 94 and the anode side 90 includes an anodeinlet 95 and an anode outlet 96. The cathode side 88 of the fuel cell68, and more specifically, the cathode inlet 93 of the cathode side 88,can be in fluid communication with, e.g., a cabin exhaust deliverysystem, and more specifically, a fuel cell inlet line of the cabinexhaust delivery system. The cathode outlet 94 is in fluid communicationwith a fuel cell outlet line of the cabin exhaust delivery system.Similarly, the anode side 90 of the fuel cell 68, and more specifically,the anode inlet 95 of the anode side 90, is in fluid communication with,e.g., a fuel delivery line of a fuel delivery system. The anode outlet96 is in fluid communication with e.g., a fuel exhaust line of the fueldelivery system. Accordingly, air may pass through the cathode side 88and fuel may pass through the anode side 90.

Returning to FIG. 1 , the electrical power system 50 includes aplurality of power controllers. Each power controller can include one ormore processors and one or more non-transitory memory devices, e.g.,embodied in a controller, and power electronics to convert electricalpower, e.g., from alternating current (AC) to direct current (DC) orvice versa, or to condition the electrical power to a desired voltage,current, or both. As depicted in FIG. 1 , the first electric machine 54has an associated power controller 55 that controls the electric powerbetween the first electric machine 54 and the power bus 52. Likewise,the second electric machine 56 has an associated power controller 57that controls the electric power between the second electric machine 56and the power bus 52. The electric energy storage system 58 also has anassociated power controller 59 that controls the electric power betweenthe electric energy storage system 58 and the power bus 52. In addition,the fuel cell assembly 60 has an associated power controller 61 thatcontrols the electric power between the fuel cell assembly 60 and thepower bus 52. Similarly, power controllers 71 can be arranged to controlthe electric power provided from the power bus 52 to the power consumingone or more electric loads 70.

For this embodiment, the electrical power system 50 is configured as adecentralized power allocation system. That is, the architecture of theelectrical power system 50 enables the power controllers to control theelectrical power outputs of their respective power sources to meet thepower demands of the power consumers collaboratively, adaptively, andwithout active supervision, e.g., from a supervisor controller.Decentralized control of electric power transmission from power sourcesto one or more power consumers can provide certain advantages, benefits,and technical effects. For instance, the decentralized electrical powerallocation systems provided herein may address the drawbacks ofconventional centralized power allocation systems and offercollaborative and adaptive control of the power outputs of the powersources to meet a power demand on a power bus applied by the one or morepower consumers. In this regard, less computing resources andcommunication networks may be needed (which has the added benefit ofreducing the weight of a vehicle), and localized control can be achievedwhilst still being collaborative with other power sources and adaptiveto meet to the power demand on the power bus. The inventive aspects of adecentralized power allocation system, which may be incorporated intothe electrical power system 50 of the aircraft 10 of FIG. 1 as well asother vehicles, will be provided below in detail.

FIG. 5 provides a system diagram of an electrical power system 200according to an example embodiment of the present disclosure. Theelectrical power system 200 is configured as a decentralized powerallocation system in FIG. 5 . The electrical power system 200 can beimplemented in a vehicle, such as the aircraft 10 of FIG. 1 , ships,trains, unmanned aerial vehicles, automobiles, etc.

As depicted in FIG. 5 , the electrical power system 200 includes adirect current power bus (or DC power bus 210), a plurality of powersource assemblies 230 electrically coupled with the DC power bus 210,and one or more electric power consumers 260 electrically coupled withthe DC power bus 210. The electrical power system 200 further includes acommunication bus 220 (shown in dashed lines in FIG. 5 ), which mayinclude one or more wired or wireless communication links. Thecommunication bus 220 enables communication between various componentsof the electrical power system 200.

For this embodiment, the plurality of power source assemblies 230include a first power source assembly 240 and a second power sourceassembly 250. Each power source assembly includes an electric powersource and a power controller. For instance, the first power sourceassembly 240 has a first power source 242 and a first power controller244. The second power source assembly 250 has a second power source 252and a second power controller 254. For this example embodiment, thefirst power source 242 is a fuel cell and the second power source 252 isan electric machine configured as an electric generator or operable in agenerator mode. As represented in FIG. 5 , the plurality of power sourceassemblies 230 can include more than two (2) power source assemblies inother example embodiments, or N-S number of power source assemblies,wherein N-S is an integer equal to or greater than two (2).

The first power source 242 and the second power source 252 areelectrically coupled with the DC power bus 210. The first powercontroller 244 controls electric power provided from the first powersource 242 to the DC power bus 210. Similarly, the second powercontroller 254 controls electric power provided from the second powersource 252 to the DC power bus 210. The first power controller 244 andthe second power controller 254 each include one or more processors andone or more non-transitory memory devices embodied in a first controller246 and a second controller 256, respectively. The first powercontroller 244 includes first power electronics 248 to convert orcondition electrical power provided from the first power source 242 tothe DC power bus 210. The first power electronics 248 can include aplurality of switches controllable in a switching scheme, for example.Similarly, the second power controller 254 includes second powerelectronics 258 to convert or condition electrical power provided fromthe second power source 252 to the DC power bus 210. The second powerelectronics 258 can include a plurality of switches controllable in aswitching scheme, for example. The first controller 246 and the secondcontroller 256 are communicatively coupled with one another (and toother components) via the communication bus 220.

The one or more electric power consumers 260 include a first powerconsumer 270 and a second power consumer 280 in this example embodiment.In some embodiments, the first power consumer 270 can represent one ormore mission critical or essential loads and the second power consumer280 can represent one or more non-essential loads. The one or moreelectric power consumers 260, or sensors or communication interfacesthereof, can be communicatively coupled with the first controller 246and the second controller 256 of the first and second power sourceassemblies 240, 250 via the communication bus 220. As represented inFIG. 5 , the one or more electric power consumers 260 can include one ormore power consumers, or N−C number of power consumer assemblies,wherein N−C is an integer equal to or greater than one (1).

In addition, for the depicted embodiment of FIG. 5 , the first powerconsumer 270 and the second power consumer 280 are both directlyelectrically coupled with the DC power bus 210. However, in otherembodiments, the first power consumer 270 and/or the second powerconsumer 280 can be indirectly electrically coupled with the DC powerbus 210. For example, an intermediate power bus and/or other powerelectronics can be positioned electrically between the DC power bus 210and the first power consumer 270 and/or the second power consumer 280.

The decentralized power allocation control aspects will now be providedwith reference to FIGS. 5, 6, and 7 . FIG. 6 provides a logic flowdiagram for allocating power to be output by the first power source 242to meet the power demand on the DC power bus 210. FIG. 7 provides alogic flow diagram for allocating power to be output by the second powersource 252 to meet the power demand on the DC power bus 210.

As shown particularly in FIG. 6 and with general reference to FIG. 5 ,the first controller 246 includes adaptive droop control logic 300 inaccordance with an adaptive droop control scheme. In executing theadaptive droop control logic 300, the one or more processors of thefirst controller 246 can regulate the power output of the first powersource 242, which as noted above, is a fuel cell in this exampleembodiment (hence the “FC” designations in FIG. 6 ).

A power feedback P_(ƒbk-FC) is input into a droop control block 304. Thepower feedback P_(ƒbk-FC) can be a measured, calculated, or predictedvalue indicating the power output of the first power source 242. Forinstance, one or more sensors can sense the voltage, frequency, and/orthe electric current proximate the first power source 242 to measure,calculate, or predict the power output of the first power source 242. Atthe droop control block 304, the power feedback P_(ƒbk-FC) is used forcorrelation purposes. Particularly, the power feedback P_(ƒbk-FC) can becorrelated with a first droop function ƒ_(drp-FC) associated with thefirst power source 242 to determine a voltage setpoint ν_(REF-FC). Thevoltage setpoint ν_(REF-FC) can be determined as the y-component of thepoint along the first droop function ƒ_(drp-FC) that corresponds withthe power feedback P_(ƒbk-FC). The first droop function ƒ_(drp-FC) orcurve represents an efficiency of the first power source 242 to generateelectrical power for a given power output of the first power source 242.

The first droop function ƒ_(drp-FC) used for the correlation can beselected from a plurality of first droop functions associated with thefirst power source 242 as represented in FIG. 6 . The first droopfunction ƒ_(drp-FC) used for correlation purposes can be selected basedat least in part on one or more operating conditions 243 (FIG. 5 )associated with the vehicle in which the electrical power system 200 isimplemented. For instance, for an aircraft, the first droop functionƒ_(drp-FC) can be selected based on a phase of flight, an altitude ofthe aircraft, a number of passengers onboard the aircraft, weatherconditions, a combination of the foregoing, etc. These noted operatingconditions may each affect the power demand on the DC power bus 210.

As one example, the plurality of first droop functions can include afirst droop function for each phase of flight, such as one for takeoff,one for climb, one for cruise, one for descent, and one for approach andlanding. As another example, the plurality of first droop functions caninclude a first droop function for different altitude ranges, such asone for zero (0) to ten thousand (10,000) feet, one for ten thousand one(10,001) to twenty thousand (20,000) feet, and one for twenty thousandone (20,001) feet and above. The altitude ranges can be defined withrespect to feet above sea level or above ground level. As yet anotherexample, the plurality of first droop functions can include a firstdroop function for different ranges of passengers onboard, such as onefirst droop function for a first range of passengers (e.g., 0 to 50passengers), one for a second range of passengers (e.g., 51 to 100passengers), and one for a third range of passengers (e.g., 101passengers and up). The plurality of first droop functions selectablefor correlation purposes can each have different slopes and/or differenty-intercepts. The first droop functions or curves each represent anefficiency of the first power source 242 to generate electrical powerfor a given power output of the first power source 242 at a given set ofoperating conditions.

As noted above, the selected first droop function ƒ_(drp-FC) can be usedto schedule or determine the voltage setpoint ν_(REF-FC) associated withthe first power source 242. More specifically, the voltage setpointν_(REF-FC) can be determined as the y-component of the point along thefirst droop function ƒ_(drp-FC) that corresponds with the power feedbackP_(ƒbk-FC). In this regard, the voltage setpoint ν_(REF-FC) is set as afunction of the power feedback P_(ƒbk-FC). The y-intercept of the firstdroop function ƒ_(drp-FC) selected for correlation purposes in FIG. 6 isdenoted as ν_(SET-FC).

As further shown in FIG. 6 , the determined voltage setpoint ν_(REF-FC)is output from the droop control block 304 and forwarded to a voltageloop of the adaptive droop control logic 300. Particularly, the voltagesetpoint ν_(REF-FC) is input into a first summation block 306 andcompared to a voltage feedback ν_(ƒbk-FC). The voltage feedbackν_(ƒbk-FC) can be a measured, calculated, or predicted value indicatingthe voltage at the first power source 242, e.g., at output terminalsthereof. A voltage difference ν_(Δ-FC) is determined at the firstsummation block 306, e.g., by subtracting the voltage setpointν_(REF-FC) from the voltage feedback ν_(ƒbk-FC) or vice versa. Thevoltage difference ν_(Δ-FC) is then input into a proportional-integralcontrol 308, which generates one or more outputs that can be input intoa switching logic control 310 that controls modulation of switchingdevices of the first power electronics 248, e.g., in a Pulse WidthModulated (PWM) switching scheme. Accordingly, a power output 312 of thefirst power source 242 is achieved. The power output 312 is affected bya disturbance, which is a power demand 212 on the DC power bus 210, asrepresented at a second summation block 314.

As shown particularly in FIG. 7 and with general reference to FIG. 5 ,the second controller 256 includes adaptive droop control logic 400 inaccordance with the adaptive droop control scheme. In executing theadaptive droop control logic 400, the one or more processors of thesecond controller 256 can regulate the power output of the second powersource 252, which as noted above, is an electric generator or electricmachine operable in a generator mode in this example embodiment (hencethe GEN″ designations in FIG. 7 ).

A power feedback P_(ƒbk-GEN) is input into a droop control block 304.The power feedback P_(ƒbk-GEN) can be a measured, calculated, orpredicted value indicating the power output of the second power source252. For instance, one or more sensors can sense the voltage, frequency,and/or the electric current proximate the second power source 252 tomeasure, calculate, or predict the power output of the second powersource 252. At the droop control block 404, the power feedbackP_(ƒbk-GEN) is used for correlation purposes. Particularly, the powerfeedback P_(ƒbk-GEN) can be correlated with a second droop functionƒ_(drp-GEN) associated with the second power source 252 to determine avoltage setpoint ν_(REF-GEN). The voltage setpoint ν_(REF-GEN) can bedetermined as the y-component of the point along the second droopfunction ƒ_(drp-GEN) that corresponds with the power feedbackP_(ƒbk-GEN). The second droop function ƒ_(drp-GEN) or curve representsan efficiency of the second power source 252 to generate electricalpower for a given power output of the second power source 252.

The second droop function ƒ_(drp-GEN) used for the correlation can beselected from a plurality of second droop functions associated with thesecond power source 252 as represented in FIG. 7 . The second droopfunction ƒ_(drp-GEN) used for correlation purposes can be selected basedat least in part on one or more operating conditions 253 (FIG. 5 )associated with the vehicle in which the electrical power system 200 isimplemented. For instance, for an aircraft, the second droop functionƒ_(drp-GEN) can be selected based on a phase of flight, an altitude ofthe aircraft, a number of passengers onboard the aircraft, weatherconditions, a combination of the foregoing, etc. These noted operatingconditions may each affect the power demand on the DC power bus 210. Theone or more operating conditions 253 received by the second controller256 of FIG. 5 can be the same as the one or more operating conditions243 received by the first controller 246 of FIG. 5 . The plurality ofsecond droop functions selectable for correlation purposes can each havedifferent slopes and/or different y-intercepts. The second droopfunctions or curves each represent an efficiency of the second powersource 252 to generate electrical power for a given power output of thesecond power source 252 at a given set of operating conditions.

As noted previously, the selected first droop function ƒ_(drp-GEN) canbe used to schedule or determine the voltage setpoint ν_(REF-GEN)associated with the second power source 252. More particularly, thevoltage setpoint ν_(REF-GEN) can be determined as the y-component of thepoint along the second droop function ƒ_(drp-GEN) that corresponds withthe power feedback P_(ƒbk-GEN). In this regard, the voltage setpointν_(REF-GEN) is set as a function of the power feedback P_(ƒbk-GEN) They-intercept of the second droop function ƒ_(drp-GEN) selected forcorrelation purposes in FIG. 7 is denoted as ν_(SET-GEN).

The voltage setpoint ν_(REF-GEN) is output from the droop control block404 and forwarded to a voltage loop of the adaptive droop control logic400. Particularly, the voltage setpoint ν_(REF-GEN) is input into afirst summation block 406 and compared to a voltage feedbackν_(ƒbk-GEN). The voltage feedback ν_(ƒbk-GEN) can be a measured,calculated, or predicted value indicating the voltage at the secondpower source 252, e.g., at output terminals thereof. A voltagedifference ν_(Δ-GEN) is determined at the first summation block 406,e.g., by subtracting the voltage setpoint ν_(REF-GEN) from the voltagefeedback V ƒbk-GEN or vice versa. The voltage difference ν_(Δ-GEN) isthen input into a proportional-integral control 408, which generates oneor more outputs that can be input into a switching logic control 410that controls modulation of switching devices of the second powerelectronics 258, e.g., in a PWM switching scheme. Accordingly, a poweroutput 412 of the second power source 252 is achieved. The power output412 is affected by a disturbance, which is the power demand 212 on theDC power bus 210, as represented at a second summation block 414.

Accordingly, each power controller of the power source assemblies 230includes executable adaptive droop control logic, e.g., similar to theadaptive droop control logic 300, 400 depicted in FIGS. 6 and 7 . When agiven power controller executes its adaptive droop control logic, theone or more processors of the given power controller cause itsassociated power electronics to control the power output of itsassociated power source. This adaptive droop control scheme executed byeach power controller of the power source assemblies 230 enablesintelligent decentralized power allocation for meeting power demands onthe DC power bus 210 applied by the electric power consumers 260.Specifically, implementation of the adaptive droop control schemeenables decentralized DC bus regulation according to the efficiencies ofthe power sources at given power outputs.

For instance, with reference to FIGS. 5 and 8 , FIG. 8 provides a graphrepresenting the first droop function ƒ_(drp-FC) associated with thefirst power source 242 overlaid with the second droop functionƒ_(drp-GEN) associated with the second power source 252 on a DC busvoltage versus power output graph. As noted above, the first droopfunction ƒ_(drp-FC) represents an efficiency of the first power source242 to generate electrical power for a given power output of the firstpower source 242 and the second droop function ƒ_(drp-GEN) represents anefficiency of the second power source 252 to generate electrical powerfor a given power output of the second power source 252. According, thedroop functions are also functions of power output efficiency η.

As shown in FIG. 8 , the droop functions have different slopes anddifferent y-intercepts, with the first droop function ƒ_(drp-FC) havinga steeper slope than the second droop function ƒ_(drp-GEN) and the firstdroop function ƒ_(drp-FC) having a greater y-intercept than the seconddroop function ƒ_(drp-GEN). Also, the droop functions intersect at apoint P_(Int) corresponding to a reference power level P_(RF).Accordingly, the first power source 242, or fuel cell for this example,is more efficient at outputting electric power at lower power levelsthan the second power source 252, or electric machine in this example.In contrast, at higher power levels, the second power source 252 is moreefficient at outputting electric power than the first power source 242.In this regard, the droop functions are coordinated so that the poweroutput of the first power source 242, or fuel cell, is greater than thepower output of the second power source 252, or electric machine, atpower levels less than the reference power level P_(RF) and so that thepower output of the second power source 252, or electric machine, isgreater than the power output of the first power source 242, or fuelcell, at power levels greater than the reference power level P_(RF).

Particularly, as shown in FIG. 8 , for a given DC bus voltage, theworking point of both the first power source 242 and the second powersource 252 will both be on the same horizontal line as the first andsecond power sources 242, 252 are electrically coupled to a common powerbus, or DC power bus 210 in this example. For instance, for a first DCbus voltage ν_(DC BUS 1), the working point of the first power source242, or fuel cell, and the working point of the second power source 252,or electric machine, are on the same horizontal line. The working pointof the first power source 242 is denoted as PT1-FC and the working pointof the second power source 252 is denoted as PT1-GEN. For the first DCbus voltage ν_(DC BUS 1), the first power source 242, or fuel cell, hasa power output of P1 while the second power source 252, or electricmachine, has a power output of P0.

Accordingly, the first power source 242 has a greater load share orpower output at the first DC bus voltage ν_(DC BUS 1) than does thesecond power source 252. The power output of P0 is equal to zero (0) inthis instance, as the y-intercept of the second droop functionƒ_(drp-GEN) is less than the first DC bus voltage ν_(DC BUS 1).Accordingly, to meet the first DC bus voltage ν_(DC BUS 1), only thefirst power source 242, or fuel cell, outputs electric power. Thus, theload share split is 100%/0%, with the first power source 242 being at100% and the second power source 252 at 0%. Advantageously, whenrelatively low power is needed, such as during ground idle or taxioperations of an aircraft, the adaptive droop control scheme allows forthe first power source 242, or fuel cell, to handle all or most of therelatively low power demand on the DC power bus 210. This takesadvantage of the physics and characteristics of the fuel cell to operateat high efficiency at low power levels whilst also saving fuel and wearon the electric machine and gas turbine engine to which the electricmachine is coupled.

For a second DC bus voltage ν_(DC BUS 2), which corresponds to a lowervoltage level than the first DC bus voltage ν_(DC BUS 1), the workingpoint of the first power source 242, or fuel cell, and the working pointof the second power source 252, or electric machine, are on the samehorizontal line. The working point of the first power source 242 isdenoted as PT2-FC and the working point of the second power source 252is denoted as PT2-GEN. For the second DC bus voltage ν_(DC BUS 2), thefirst power source 242, or fuel cell, and the second power source 252,or electric machine, both have the same power output, which correspondsto the reference power level P_(RF). Accordingly, the first power source242 and the second power source 252 have a same load share or poweroutput at the second DC bus voltage ν_(DC BUS 2) Thus, the load sharesplit is 50%/50%, with the first power source 242 being at 50% and thesecond power source 252 being at 50% to meet the power demand on the DCpower bus 210.

Further, for a third DC bus voltage ν_(DC BUS 3), which corresponds to alower voltage level than the second DC bus voltage ν_(DC BUS 2), theworking point of the first power source 242, or fuel cell, and theworking point of the second power source 252, or electric machine, areon the same horizontal line. The working point of the first power source242 is denoted as PT3-FC and the working point of the second powersource 252 is denoted as PT3-GEN. For the third DC bus voltageν_(DC BUS 3), the first power source 242, or fuel cell, has a poweroutput of P2 while the second power source 252, or electric machine, hasa power output of P3, which is greater than the power output of P2.

Accordingly, the second power source 252 has a greater load share orpower output at the third DC bus voltage ν_(DC BUS 3) than does thefirst power source 242. The load share split can be 40%/60%, with thefirst power source 242 being at 40% and the second power source 252 at60%, for example. Advantageously, when relatively high power is needed,such as during flight operations of an aircraft, the adaptive droopcontrol scheme allows for the second power source 252, or electricmachine mechanically coupled with a gas turbine engine, to handle mostof the relatively high power demand on the DC power bus 210. This takesadvantage of the physics and characteristics of the electric machine tooperate at high efficiency at high power levels whilst also using thefuel cell in part to meet the power demand on the DC power bus 210.

Accordingly, the power allocation for the power sources is set accordingto the characteristics of the droop functions, such as their slopes,y-intercepts, and overall shapes. For the depicted embodiment of FIG. 8, as the droop functions converge toward one another, the load sharebetween the first power source 242 and the second power source 252becomes more balanced, as represented at the second DC bus voltageν_(DC BUS 2). Conversely, as the droop functions diverge away from oneanother, the load share between the first power source 242 and thesecond power source 252 becomes less balanced, as represented at thefirst DC bus voltage ν_(DC BUS 1) and the third DC bus voltageν_(DC BUS 3).

The droop functions depicted in FIGS. 6, 7, and 8 , are linearfunctions. However, one or more of the droop functions can be non-linearfunctions in other example embodiments. For instance, FIG. 9 provides agraph representing a non-linear first droop function ƒ_(drp-FC)associated with the first power source 242 overlaid with the seconddroop function ƒ_(drp-GEN) associated with the second power source 252on a DC bus voltage versus power output graph. The non-linear firstdroop function ƒ_(drp-FC) may better represent the efficiency of thefirst power source 242, or fuel cell, to output electric power at agiven power output. Further, the second droop function ƒ_(drp-GEN) maybe linear, but may be a piecewise linear function. For this exampleembodiment, the piecewise linear second droop function ƒ_(drp-GEN)includes a first segment having a first slope and a second segmenthaving a second slope that is different than the first slope. For thisexample, the first segment is steeper than the second segment of thesecond droop function ƒ_(drp-GEN). Such a piecewise linear second droopfunction ƒ_(drp-GEN) having various slopes may better represent theefficiency of the second power source 252, or electric machine, tooutput electric power at a given power output. The droop functions canhave other curves or shapes as well, such as polynomial shapes.

FIG. 10 provides a system diagram of an electrical power system 201according to another example embodiment of the present disclosure. Theelectrical power system 201 is configured as a decentralized powerallocation system in FIG. 10 . The electrical power system 201 of FIG.10 can be implemented in a vehicle, such as the aircraft 10 of FIG. 1 ,ships, trains, unmanned aerial vehicles, automobiles, etc. Theelectrical power system 201 of FIG. 10 is configured in a similar manneras the electrical power system 200 of FIG. 5 , and therefore, like partswill be identified with like numerals with it being understood that thedescription of the like parts of the electrical power system 200 appliesto the electrical power system 201 unless otherwise noted. Notably, theelectrical power system 201 of FIG. 10 includes an alternating currentpower bus (or AC power bus 215) to which the plurality of power sourceassemblies 230 and the one or more electric power consumers 260 areelectrically coupled. Single or multiphase power can be transmittedalong the AC power bus 215.

In addition, for the depicted embodiment of FIG. 10 , the first powerconsumer 270 and the second power consumer 280 are both directlyelectrically coupled with the AC power bus 215. However, in otherembodiments, the first power consumer 270 and/or the second powerconsumer 280 can be indirectly electrically coupled with the AC powerbus 215. For example, an intermediate power bus and/or other powerelectronics can be positioned electrically between the AC power bus 215and the first power consumer 270 and/or the second power consumer 280.

For the electrical power system 201 of FIG. 10 having the AC power bus215, the adaptive droop control scheme is implemented in a similarmanner as described above with reference to the DC power bus 210 of FIG.5 , except as provided below. As will be appreciated, a sinusoidalvoltage waveform on an AC power bus has both a frequency and anamplitude. The frequency of a voltage waveform is highly coupled withactive power, or power that is utilized and consumed for useful work inelectrical systems. The amplitude of a voltage waveform is highlycoupled with reactive power, or power that “bounces” back and forthbetween the power source(s) and power consumer(s) in electrical systems.Accordingly, active power is more sensitive to changes in frequency onthe AC power bus 215 while reactive power is more sensitive to changesin amplitude.

With these considerations in mind, the decentralized power allocationcontrol aspects will now be provided with reference to FIGS. 10, 11, and12 . FIG. 11 provides a logic flow diagram for allocating power to beoutput by the first power source 242, or fuel cell, to meet the powerdemand on the AC power bus 215. FIG. 12 provides a logic flow diagramfor allocating power to be output by the second power source 252, orelectric machine, to meet the power demand on the AC power bus 215.

As shown particularly in FIG. 11 and with general reference to FIG. 10 ,the first controller 246 includes adaptive droop control logic 800 inaccordance with an adaptive droop control scheme for AC power bussystems. In executing the adaptive droop control logic 800, the one ormore processors of the first controller 246 can regulate the poweroutput of the first power source 242, which as noted above, is a fuelcell in this example embodiment (hence the “FC” designations in FIG. 11).

The adaptive droop control logic 800 includes active power droopcontrol. As depicted, a power feedback P_(ƒbk-FC), which relates toactive power, is input into an active power droop control block 804. Thepower feedback P_(ƒbk-FC) can be a measured, calculated, or predictedvalue indicating the active power output of the first power source 242.For instance, one or more sensors can sense the voltage, frequency,and/or the electric current proximate the first power source 242 tomeasure, calculate, or predict the active power output of the firstpower source 242. At the active power droop control block 804, the powerfeedback P_(ƒbk-FC) is used for correlation purposes. Particularly, thepower feedback P_(ƒbk-FC) can be correlated with a first active droopfunction ƒ_(drp-FC-A) associated with the first power source 242 todetermine a frequency setpoint ƒ_(REF-FC).

The first active droop function ƒ_(drp-FC-A) used for the correlationcan be selected from a plurality of first active droop functionsassociated with the first power source 242. The first active droopfunction ƒ_(drp-FC-A) can be selected based at least in part on one ormore operating conditions 243 (FIG. 10 ) associated with the vehicle inwhich the electrical power system 201 is implemented. For instance, foran aircraft, the first active droop function ƒ_(drp-FC-A) can beselected based on a phase of flight, altitude of the aircraft, number ofpassengers onboard the aircraft, weather conditions, a combination ofthe foregoing, etc. The first droop functions or curves represent anefficiency of the first power source 242 to generate electrical powerfor a given power output of the first power source 242 at a given set ofoperating conditions.

The selected first active droop function ƒ_(drp-FC-A) can be used toschedule or determine the frequency setpoint ƒ_(REF-FC) associated withthe first power source 242. More particularly, the frequency setpointƒ_(REF-FC) can be determined as the y-component of the point along thefirst active droop function ƒ_(drp-FC-A) that corresponds with the powerfeedback P_(ƒbk-FC). In this regard, the frequency setpoint ƒ_(REF-FC)is set as a function of the power feedback P_(ƒbk-FC). The y-interceptof the first active droop function ƒ_(drp-FC-A) selected for correlationpurposes in FIG. 11 is denoted as ƒ_(SET-FC).

The frequency setpoint ƒ_(REF-FC) is output from the droop control block804 and input into a first summation block 806 and compared to afrequency feedback ƒ_(ƒbk-FC). The frequency feedback ƒ_(ƒbk-FC) can bea measured, calculated, or predicted value indicating the frequency atthe first power source 242, e.g., at output terminals thereof. Afrequency difference ƒ_(Δ-FC) is determined at the first summation block806, e.g., by subtracting the frequency setpoint ƒ_(REF-FC) from thefrequency feedback ƒ_(ƒbk-FC) or vice versa.

As further shown in FIG. 11 , for AC power bus systems, the adaptivedroop control logic 800 includes reactive power droop control inaddition to the active power droop control disclosed above. Asillustrated, a power feedback Q_(ƒbk-FC), which relates to reactivepower, is input into a reactive power droop control block 818. The powerfeedback Q_(ƒbk-FC) can be a measured, calculated, or predicted valueindicating the reactive power at the first power source 242, or ratherthe power that moves back and forth between the first power source 242and the one or more electric power consumers 260. For instance, avarmeter can be used to measure, calculate, or predict the reactivepower at the first power source 242. At the reactive power droop controlblock 818, the power feedback Q_(ƒbk-FC) is used for correlationpurposes. Specifically, the power feedback Q_(ƒbk-FC) can be correlatedwith a first reactive droop function ƒ_(drp-FC-R) associated with thefirst power source 242 to determine a voltage amplitude setpointν_(REF_AC-FC).

The first reactive droop function ƒ_(drp-FC-R) used for the correlationcan be selected from a plurality of first reactive droop functionsassociated with the first power source 242. The first reactive droopfunction ƒ_(drp-FC-R) can be selected based at least in part on one ormore operating conditions 243 (FIG. 10 ) associated with the vehicle inwhich the electrical power system 201 is implemented. For instance, foran aircraft, the first reactive droop function ƒ_(drp-FC-R) can beselected based on a phase of flight, altitude of the aircraft, number ofpassengers onboard the aircraft, weather conditions, a combination ofthe foregoing, etc.

The selected first reactive droop function ƒ_(drp-FC-R) can be used toschedule or determine the voltage amplitude setpoint ν_(REF_AC-FC)associated with the first power source 242. More particularly, thevoltage amplitude setpoint ν_(REF_AC-FC) can be determined as they-component of the point along the first reactive droop functionƒ_(drp-FC)-R that corresponds with the power feedback Q_(ƒbk-FC). Inthis regard, the voltage amplitude setpoint ν_(REF_AC-FC) is set as afunction of the power feedback Q_(ƒbk-FC), which corresponds to reactivepower feedback. The y-intercept of the first reactive droop functionƒ_(drp-FC-R) selected for correlation purposes in FIG. 11 is denoted asν_(SET-FC). The power feedback Q_(ƒbk-FC) is bound by an inductive limit−Q_(Max) and a capacitive limit Q_(Max).

The voltage amplitude setpoint ν_(REF_AC-FC) is output from the reactivepower droop control block 818 and input into a second summation block820. The voltage amplitude setpoint ν_(REF_AC-FC) is compared to avoltage amplitude feedback ƒ_(ƒbk_AC-FC) at the second summation block820. The voltage amplitude feedback ƒ_(ƒbk_AC-FC) can be a measured,calculated, or predicted value indicating the voltage amplitude at thefirst power source 242, e.g., at output terminals thereof. A voltageamplitude difference ν_(Δ-FC) is determined at the second summationblock 820, e.g., by subtracting the voltage amplitude setpointν_(REF_AC-FC) from the voltage amplitude feedback ƒƒ_(bk_AC-FC) or viceversa.

The frequency difference ƒ_(Δ-FC) and the voltage amplitude differenceν_(Δ-FC) are input into a voltage synthesizer 808, which generates oneor more outputs (e.g., a modulation index) that can be input into aswitching logic control 810 that controls modulation of switchingdevices of the first power electronics 248, e.g., in a PWM switchingscheme. Accordingly, a power output 812 of the first power source 242 isachieved. The power output 812 has an active power component and areactive power component. The power output 812 is affected by adisturbance, which is a power demand 217 on the AC power bus 215, asrepresented at a third summation block 814.

As shown particularly in FIG. 12 and with general reference to FIG. 10 ,the second controller 256 includes adaptive droop control logic 900 inaccordance with the adaptive droop control scheme. In executing theadaptive droop control logic 900, the one or more processors of thesecond controller 256 can regulate the power output of the second powersource 252, which as noted above, is an electric generator or electricmachine operable in a generator mode in this example embodiment (hencethe GEN″ designations in FIG. 12 ).

Like the adaptive droop control logic 800 (FIG. 11 ) associated with thefirst power source assembly 240, the adaptive droop control logic 900associated with the second power source assembly 250 includes bothactive power droop control and reactive droop control. For the activedroop control aspect of the adaptive droop control logic 900, a powerfeedback P_(ƒbk-GEN), which relates to active power, is input into anactive power droop control block 904. The power feedback P_(ƒbk-GEN) canbe a measured, calculated, or predicted value indicating the activepower output of the second power source 252. For instance, one or moresensors can sense the voltage, frequency, and/or the electric currentproximate the second power source 252 to measure, calculate, or predictthe active power output of the second power source 252. At the activepower droop control block 904, the power feedback P_(ƒbk-GEN) is usedfor correlation purposes. Specifically, the power feedback P_(ƒbk-GEN)can be correlated with a second active droop function ƒ_(drp-GEN-A)associated with the second power source 252 to determine a frequencysetpoint ƒ_(REF-GEN).

The second active droop function ƒ_(drp-GEN-A) used for the correlationcan be selected from a plurality of second active droop functionsassociated with the second power source 252. The second active droopfunction ƒ_(drp-GEN-A) can be selected based at least in part on one ormore operating conditions 253 (FIG. 10 ) associated with the vehicle inwhich the electrical power system 201 is implemented. For instance, foran aircraft, the second active droop function ƒ_(drp-GEN-A) can beselected based on a phase of flight, altitude of the aircraft, number ofpassengers onboard the aircraft, weather conditions, a combination ofthe foregoing, etc. The second droop functions or curves represent anefficiency of the second power source 252 to generate electrical powerfor a given power output of the second power source 252. The one or moreoperating conditions 253 received by the second controller 256 of FIG.10 can be the same as the one or more operating conditions 243 receivedby the first controller 246 of FIG. 10 .

As noted above, the selected second active droop function ƒ_(drp-GEN-A)can be used to schedule or determine the frequency setpoint ƒREF-GENassociated with the second power source 252. More particularly, thefrequency setpoint ƒ_(REF-GEN) can be determined as the y-component ofthe point along the second active droop function ƒ_(drp-GEN-A) thatcorresponds with the power feedback P_(ƒbk-GEN). In this regard, thefrequency setpoint ƒ_(REF-GEN) is set as a function of the powerfeedback P_(ƒbk-GEN). The y-intercept of the second active droopfunction ƒ_(drp-GEN-A) selected for correlation purposes in FIG. 12 isdenoted as ƒ_(SET-GEN).

The frequency setpoint ƒ_(REF-GEN) is output from the droop controlblock 904 and input into a first summation block 906 and compared to afrequency feedback ƒ_(ƒbk-GEN). The frequency feedback ƒ_(ƒbk-GEN) canbe a measured, calculated, or predicted value indicating the frequencyat the second power source 252, e.g., at output terminals thereof. Afrequency difference ƒ_(Δ-GEN) is determined at the first summationblock 906, e.g., by subtracting the frequency setpoint ƒ_(REF-GEN) fromthe frequency feedback ƒ_(ƒbk-GEN) or vice versa.

As noted above, the adaptive droop control logic 900 includes reactivepower droop control in addition to the active power droop controldisclosed above. As illustrated, a power feedback Q_(ƒbk-GEN), whichrelates to reactive power, is input into a reactive power droop controlblock 918. The power feedback Q_(ƒbk-GEN) can be a measured, calculated,or predicted value indicating the reactive power at the second powersource 252, or rather the power that moves back and forth between thesecond power source 252 and the one or more electric power consumers260. A varmeter can be used to measure, calculate, or predict thereactive power at the second power source 252. At the reactive powerdroop control block 918, the power feedback Q_(ƒbk-GEN) is used forcorrelation purposes. Particularly, the power feedback Q_(ƒbk-GEN) canbe correlated with a second reactive droop function ƒ_(drp-GEN-R)associated with the second power source 252 to determine a voltageamplitude setpoint ν_(REF_AC-GEN).

The second reactive droop function ƒ_(drp-GEN-R) used for thecorrelation can be selected from a plurality of second reactive droopfunctions associated with the second power source 252. The secondreactive droop function ƒ_(drp-GEN-R) can be selected based at least inpart on one or more operating conditions 253 (FIG. 10 ) associated withthe vehicle in which the electrical power system 201 is implemented. Forinstance, for an aircraft, the second reactive droop functionƒ_(drp-GEN-R) can be selected based on a phase of flight, altitude ofthe aircraft, number of passengers onboard the aircraft, weatherconditions, a combination of the foregoing, etc.

The selected second reactive droop function ƒ_(drp-GEN-R) can be used toschedule or determine the voltage amplitude setpoint ν_(REF_AC-GEN)associated with the second power source 252. More specifically, thevoltage amplitude setpoint ν_(REF_AC-GEN) can be determined as they-component of the point along the second reactive droop functionƒ_(drp-GEN-R) that corresponds with the power feedback Q_(ƒbk-GEN). Inthis regard, the voltage amplitude setpoint ν_(REF_AC-GEN) is set as afunction of the power feedback Q_(ƒbk-GEN), which corresponds toreactive power feedback. The y-intercept of the second reactive droopfunction ƒ_(drp-GEN-R) selected for correlation purposes in FIG. 12 isdenoted as ν_(SET-GEN). The power feedback Q_(ƒbk-GEN) is bound by aninductive limit −Q_(Max) and a capacitive limit Q_(Max).

The voltage amplitude setpoint ν_(REF_AC-GEN) is output from thereactive droop control block 918 and input into a second summation block920. The voltage amplitude setpoint ν_(REF_AC-GEN) is compared to avoltage amplitude feedback ƒ_(ƒbk_AC-GEN) at the second summation block920. The voltage amplitude feedback ƒ_(ƒbk_AC-GEN) can be a measured,calculated, or predicted value indicating the voltage amplitude at thesecond power source 252, e.g., at output terminals thereof. A voltageamplitude difference ν_(Δ-GEN) is determined at the second summationblock 920, e.g., by subtracting the voltage amplitude setpointν_(REF_AC-GEN) from the voltage amplitude feedback ƒ_(ƒbk_AC-GEN) orvice versa.

The frequency difference ƒ_(Δ-GEN) and the voltage amplitude differenceν_(Δ-GEN) are input into a voltage synthesizer 908, which generates oneor more outputs (e.g., a modulation index) that can be input into aswitching logic control 910 that controls modulation of switchingdevices of the second power electronics 258, e.g., in a PWM switchingscheme. Accordingly, a power output 912 of the second power source 252is achieved. The power output 912 has an active power component and areactive power component. The power output 912 is affected by adisturbance, which is the power demand 217 on the AC power bus 215, asrepresented at a third summation block 914. In alternative embodiments,the frequency difference ƒ_(Δ-GEN) and the voltage amplitude differenceν_(Δ-GEN) are each input into respective proportional-integral controlsand then fed into the switching logic control 910.

Accordingly, each power controller of the power source assemblies 230includes executable adaptive droop control logic, e.g., similar to theadaptive droop control logic 800, 900 depicted in FIGS. 11 and 12 . Whena given power controller executes its adaptive droop control logic, theone or more processors of the given power controller cause itsassociated power electronics to control the power output of itsassociated power source. This adaptive droop control scheme executed byeach power controller of the power source assemblies 230 enablesintelligent decentralized power allocation for meeting power demands onthe AC power bus 215 applied by the electric power consumers 260.Specifically, implementation of the adaptive droop control schemeenables decentralized AC bus regulation according to the efficiencies ofthe power sources at given power outputs.

For instance, with reference to FIGS. 10 and 13 , FIG. 13 provides agraph representing the first droop function ƒ_(drp-FC-A) associated withthe first power source 242 overlaid with the second droop functionƒ_(drp-GEN-A) associated with the second power source 252 on an AC busfrequency versus power output graph. The first droop functionƒ_(drp-FC-A) represents an efficiency of the first power source 242 togenerate active electrical power for a given power output of the firstpower source 242 and the second droop function ƒ_(drp-GEN-A) representsan efficiency of the second power source 252 to generate activeelectrical power for a given power output of the second power source252. According, the droop functions are also functions of power outputefficiency η.

As shown in FIG. 13 , the active power droop functions have differentslopes, with the first droop function ƒ_(drp-FC-A) having a steeperslope than the second droop function ƒ_(drp-GEN-A). Also, the droopfunctions intersect at a point P_(Int) corresponding to a referencepower level P_(RF). The first power source 242, or fuel cell for thisexample, is more efficient at outputting electric power at lower powerlevels than the second power source 252, or electric machine in thisexample. In contrast, at higher power levels, the second power source252 is more efficient at outputting electric power than the first powersource 242. In this regard, the droop functions are coordinated so thatthe power output of the first power source 242, or fuel cell, is greaterthan the power output of the second power source 252, or electricmachine, at power levels less than the reference power level P_(RF) andso that the power output of the second power source 252, or electricmachine, is greater than the power output of the first power source 242,or fuel cell, at power levels greater than the reference power levelP_(RF).

Particularly, as shown in FIG. 13 , for a given AC bus frequency, theworking point of both the first power source 242 and the second powersource 252 will both be on the same horizontal line as the first andsecond power sources 242, 252 are electrically coupled to a common powerbus, or AC power bus 215 in this example. For instance, for a first ACbus frequency ƒ_(AC BUS 1), the working point of the first power source242, or fuel cell, and the working point of the second power source 252,or electric machine, are on the same horizontal line. The working pointof the first power source 242 is denoted as PT1-FC-A and the workingpoint of the second power source 252 is denoted as PT1-GEN-A. For thefirst AC bus frequency ƒ_(AC BUS 1), the first power source 242, or fuelcell, has a power output of P1 while the second power source 252, orelectric machine, has a power output of P0.

Accordingly, the first power source 242 has a greater load share orpower output at the first AC bus frequency ƒ_(AC BUS 1) than does thesecond power source 252. The power output of P0 is equal to zero (0) inthis instance, as the y-intercept of the second droop functionƒ_(drp-GEN-A) is less than the first AC bus frequency ƒ_(AC BUS 1).Accordingly, to meet the first AC bus frequency ƒ_(AC BUS 1), only thefirst power source 242, or fuel cell, outputs electric power. Thus, theload share split is 100%/0%, with the first power source 242 being at100% and the second power source 252 at 0%. Advantageously, whenrelatively low power is needed, such as during ground idle or taxioperations of an aircraft, the adaptive droop control scheme allows forthe first power source 242, or fuel cell, to handle all or most of therelatively low power demand on the AC power bus 215. This takesadvantage of the physics and characteristics of the fuel cell to operateat high efficiency at low power levels whilst also saving fuel and wearon the electric machine and gas turbine engine to which the electricmachine is coupled.

For a second AC bus frequency ƒ_(AC BUS 2), which corresponds to a lowerfrequency level than the first AC bus frequency ƒ_(AC BUS 2), theworking point of the first power source 242, or fuel cell, and theworking point of the second power source 252, or electric machine, areon the same horizontal line. The working point of the first power source242 is denoted as PT2-FC-A and the working point of the second powersource 252 is denoted as PT2-GEN-A. For the second AC bus frequencyƒ_(AC BUS 2), the first power source 242, or fuel cell, and the secondpower source 252, or electric machine, both have the same power output,which corresponds to the reference power level P_(RF). Accordingly, thefirst power source 242 and the second power source 252 have a same loadshare or power output at the second AC bus frequency ƒ_(AC BUS 2). Thus,the load share split is 50%/50%, with the first power source 242 beingat 50% and the second power source 252 being at 50% to meet the powerdemand on the AC power bus 215.

Further, for a third AC bus frequency ƒ_(AC Bus 3), which corresponds toa lower frequency level than the second AC bus frequency ƒ_(AC BUS 2),the working point of the first power source 242, or fuel cell, and theworking point of the second power source 252, or electric machine, areon the same horizontal line. The working point of the first power source242 is denoted as PT3-FC-A and the working point of the second powersource 252 is denoted as PT3-GEN-A. For the third AC bus frequencyƒ_(AC BUS 3), the first power source 242, or fuel cell, has a poweroutput of P2 while the second power source 252, or electric machine, hasa power output of P3, which is greater than the power output of P2.

Accordingly, the second power source 252 has a greater load share orpower output at the third AC bus frequency ƒ_(AC BUS 3) than does thefirst power source 242. The load share split can be 40%/60%, with thefirst power source 242 being at 40% and the second power source 252 at60%, for example. Advantageously, when relatively high power is needed,such as during flight operations of an aircraft, the adaptive droopcontrol scheme allows for the second power source 252, or electricmachine mechanically coupled with a gas turbine engine, to handle mostof the relatively high power demand on the AC power bus 215. This takesadvantage of the physics and characteristics of the electric machine tooperate at high efficiency at high power levels whilst also using thefuel cell in part to meet the power demand on the AC power bus 215.

Accordingly, the power allocation for the power sources is set accordingto the characteristics of the droop functions, such as their slopes,y-intercepts, and overall shapes. For the depicted embodiment of FIG. 13, as the droop functions converge toward one another, the load sharebetween the first power source 242 and the second power source 252becomes more balanced, as represented at the second AC bus frequencyƒ_(AC BUS 2). Conversely, as the droop functions diverge away from oneanother, the load share between the first power source 242 and thesecond power source 252 becomes less balanced, as represented at thefirst AC bus frequency ƒ_(AC BUS 1) and the third AC bus frequencyƒ_(AC BUS 3).

It will be appreciated that, like the active power allocation schemedisclosed above and represented in FIG. 13 , reactive power allocationfor the power sources can be set according to the coordination andcharacteristics of the reactive droop functions, such as their slopes,y-intercepts, and overall shapes.

Moreover, in some embodiments, the reactive power control aspects of theadaptive droop control logic 800, 900 are optionally not implemented ornot a part of the adaptive droop control logic 800, 900. In suchembodiments, a voltage regulating device can be employed to regulate thevoltage on the AC power bus 215.

Further, the droop functions depicted in FIGS. 11, 12, and 13 , arelinear functions. However, one or more of the droop functions can benon-linear functions in other example embodiments. In other embodiments,one or more of the droop functions may be piecewise linear functions,polynomial functions, etc.

In accordance with the adaptive droop control schemes disclosed herein,such control schemes can also be deemed “adaptive” in that droopfunctions selected for correlation purposes can be selected or otherwiseadjusted based on a health status of one or more of the power sources orcomponents associated therewith, such as their respective powercontrollers, and particularly, their respective power electronics.

By way of example and with reference to FIG. 5 , for a given powerdemand and operating conditions of the vehicle in with the electricalpower system 200 is implemented, the one or more processors of the firstcontroller 246 can receive a health status 245 associated with the firstpower source 242 and/or the first power controller 244, wherein thehealth status 245 indicates a degree of degradation from a baselinehealth status, such as a new condition first power source and/or newcondition first power electronics. Likewise, for a given power demandand operating conditions of the vehicle in which the electrical powersystem 200 is implemented, the one or more processors of the secondcontroller 256 can receive a health status 255 associated with thesecond power source 252 and/or the second power controller 254, whereinthe health status 255 indicates a degree of degradation from a baselinehealth status, such as a new condition second power source and/or newcondition second power electronics.

With reference now to FIGS. 14 and 15 in addition to FIG. 5 , FIG. 14provides a graph depicting a first droop function ƒ_(drp-FC-1)associated with the first power source 242 overlaid with a second droopfunction ƒ_(drp-GEN-1) associated with the second power source 252 ofthe electrical power system 200 of FIG. 5 , the first droop functionƒ_(drp-FC-1) and the second droop function ƒ_(drp-GEN-1) being selectedbased on a first set of operating conditions and at a first time t1 atwhich the first power source 242 has a first health status indicating afirst level of health and the second power source 252 has a first healthstatus indicating a first level of health. FIG. 15 provides a graphdepicting a first droop function ƒ_(drp-FC-2) associated with the firstpower source 242 overlaid with a second droop function ƒ_(drp-GEN-2)associated with the second power source 252 of the electrical powersystem 200 of FIG. 5 , the first droop function ƒ_(drp-FC-2) and thesecond droop function ƒ_(drp-GEN-2) being selected based on the firstset of operating conditions (the same operating conditions as in FIG. 14) and at a second time t2 that is later in time than time t1 of FIG. 14. At time t2, the first power source 242 has a second health statusindicating a second level of health and the second power source 252 hasa second health status indicating a second level of health. The secondhealth status of the first and second power sources 242, 252 indicatesgreater deterioration from a baseline health status compared to thefirst health status of the first and second power sources 242, 252.

In comparing the first droop function of FIG. 14 with the first droopfunction of FIG. 15 , the first droop function of FIG. 14 , whichrepresents the efficiency of the first power source at time t1 and forthe first set of operating conditions, is steeper than the first droopfunction of FIG. 15 , which represents the efficiency of the first powersource at time t2 and for the first set of operating conditions. In thisregard, the first droop function selected for correlation purposes isadapted or intelligently selected as the first power source deterioratesover time. Likewise, in comparing the second droop function of FIG. 14with the second droop function of FIG. 15 , the second droop function ofFIG. 14 , which represents the efficiency of the second power source attime t1 and for the first set of operating conditions, is steeper thanthe second droop function of FIG. 15 , which represents the efficiencyof the second power source at time t2 and for the first set of operatingconditions. Accordingly, the second droop function selected forcorrelation purposes is adapted or intelligently selected as the secondpower source deteriorates over time.

As will further be appreciated by comparing FIG. 14 and FIG. 15 , thefirst and second droop functions of FIG. 14 diverge more significantlyas they move away from the reference power level P_(RF) than do thefirst and second droop functions of FIG. 15 . Moreover, the referencepower level P_(RF) has shifted to the right in FIG. 15 along the X-axisfrom its position in FIG. 14 . These differences indicate the adaptivepower allocation of the power sources over time made possible by theadaptive droop control scheme when accounting for the health status ofthe power sources. It will be appreciated that the teachings relating toaccounting for health status in selecting a droop function forcorrelation purposes applies equally to AC power bus systems, such asthe electrical power system 201 of FIG. 10 .

FIG. 16 provides a flow diagram of a method 1000 of operating adecentralized power allocation system for an aircraft. For instance, themethod 1000 can be utilized to operate the electrical power systems 200,201 of FIG. 5 or FIG. 10 .

At 1002, the method 1000 includes controlling a first power output of afirst power source to meet a power demand on a power bus applied by oneor more power consumers, the first power output being controlled basedat least in part on a correlation of a power feedback of the first powersource and a first droop function that represents an efficiency of thefirst power source to generate electrical power for a given power outputof the first power source. For instance, a first power controllerassociated with the first power source can control the first poweroutput of the first power source. One or more processors of the firstpower controller can receive the power feedback of the first powersource and can correlate the power feedback to the first droop function.As one example, the power feedback can be compared to a power setpointto determine a power difference. The power difference can be used toadjust, if necessary, the power feedback from a previous timestep of theone or more processors. The adjusted power feedback is then correlatedwith the first droop function.

In implementations where the power bus is a direct current power bus, avoltage setpoint is determined based on the correlation between theadjusted power feedback and the first droop function. First powerelectronics of the first power controller (e.g., switches thereof) canbe controlled based on the voltage setpoint to output the first poweroutput. In implementations where the power bus is an alternating currentpower bus, a frequency setpoint is determined based on the correlationbetween the adjusted power feedback and the first droop function. Thefirst power electronics of the first power controller (e.g., switchesthereof) can be controlled based on the frequency setpoint to output thefirst power output. In some instances, the first power output is notequal to zero (0). In such instances, the first power source has a loadshare in meeting the power demand on the power bus. In other instances,the first power output can be equal to zero. In this regard, in someinstances, the load share of the first power source in meeting the powerdemand on the power bus is zero (0).

At 1004, the method 1000 includes controlling a second power output of asecond power source to meet the power demand on the power bus, thesecond power output being controlled based at least in part on acorrelation of a power feedback of the second power source and a seconddroop function that represents an efficiency of the second power sourceto generate electrical power for a given power output of the secondpower source, and wherein the first droop function and the second droopfunction are coordinated so that the first power output of the firstpower source is greater than the second power output of the second powersource at power levels less than a reference power level and so that thesecond power output of the second power source is greater than the firstpower output of the first power source at power levels greater than thereference power level.

For instance, a second power controller associated with the second powersource can control the second power output of the second power source.One or more processors of the second power controller can receive thepower feedback of the second power source and can correlate the powerfeedback to the second droop function. As one example, the powerfeedback can be compared to a power setpoint to determine a powerdifference. The power difference can be used to adjust, if necessary,the power feedback from a previous timestep of the one or moreprocessors of the second power controller. The adjusted power feedbackis then correlated with the second droop function.

In implementations where the power bus is a direct current power bus, avoltage setpoint is determined based on the correlation between theadjusted power feedback and the second droop function. Second powerelectronics of the second power controller (e.g., switches thereof) canbe controlled based on the voltage setpoint to output the second poweroutput. In implementations where the power bus is an alternating currentpower bus, a frequency setpoint is determined based on the correlationbetween the adjusted power feedback and the second droop function. Thesecond power electronics of the second power controller (e.g., switchesthereof) can be controlled based on the frequency setpoint to output thesecond power output. In some instances, the second power output is notequal to zero (0). In such instances, the second power source has a loadshare in meeting the power demand on the power bus. In other instances,the second power output can be equal to zero. In this regard, in someinstances, the load share of the second power source in meeting thepower demand on the power bus is zero (0).

In some implementations, the power bus is an alternating current powerbus, and wherein the reference power level corresponds to a point atwhich the first droop function and the second droop function intersect,wherein the first and second droop functions are represented asfunctions of a frequency of the alternating current power bus versuspower output of the first and second power sources. In otherimplementations, the power bus is a direct current power bus, andwherein the reference power level corresponds to a point at which thefirst droop function and the second droop function intersect, whereinthe first and second droop functions are represented as functions of avoltage of the direct current power bus versus power output of the firstand second power sources.

In some implementations, the first power source is a fuel cell assemblyand the second power source is an electric machine mechanically coupledwith a gas turbine engine. In other implementations, the first powersource is a first fuel cell assembly and the second power source is asecond fuel assembly. In some further implementations, the first powersource is a first electric machine mechanically coupled with a first gasturbine engine and the second power source is a second electric machinemechanically coupled with a second gas turbine engine.

FIG. 17 provides a computing system 1100 according to exampleembodiments of the present disclosure. The computing devices or elementsdescribed herein, such as the controllers 246, 256 (FIG. 5 and FIG. 10), may include various components and perform various functions of thecomputing system 1100 provided below.

The computing system 1100 can include one or more computing device(s)1110. The computing device(s) 1110 can include one or more processor(s)1110A and one or more memory device(s) 1110B. The one or moreprocessor(s) 1110A can include any suitable processing device, such as amicroprocessor, microcontroller, integrated circuit, logic device,and/or other suitable processing device. The one or more memorydevice(s) 1110B can include one or more computer-executable orcomputer-readable media, including, but not limited to, non-transitorycomputer-readable medium, RAM, ROM, hard drives, flash drives, and/orother memory devices.

The one or more memory device(s) 1110B can store information accessibleby the one or more processor(s) 1110A, including computer-readableinstructions 1110C that can be executed by the one or more processor(s)1110A. The instructions 1110C can be any set of instructions that, whenexecuted by the one or more processor(s) 1110A, cause the one or moreprocessor(s) 1110A to perform operations, such executing adaptive droopcontrol schemes. The instructions 1110C can be software written in anysuitable programming language or can be implemented in hardware.Additionally, and/or alternatively, the instructions 1110C can beexecuted in logically and/or virtually separate threads on processor(s)1110A. The memory device(s) 1110B can further store data 1110D that canbe accessed by the processor(s) 1110A. For example, the data 1110D caninclude models, lookup tables, databases, etc., and particularly, setsof droop control functions.

The computing device(s) 1110 can also include a network interface 1110Eused to communicate, for example, with the other components of thecomputing system 1100 (e.g., via a communication network). The networkinterface 1110E can include any suitable components for interfacing withone or more network(s), including for example, transmitters, receivers,ports, controllers, antennas, and/or other suitable components.

The technology discussed herein makes reference to computer-basedsystems and actions taken by and information sent to and fromcomputer-based systems. One of ordinary skill in the art will recognizethat the inherent flexibility of computer-based systems allows for agreat variety of possible configurations, combinations, and divisions oftasks and functionality between and among components. For instance,processes discussed herein can be implemented using a single computingdevice or multiple computing devices working in combination. Databases,memory, instructions, and applications can be implemented on a singlesystem or distributed across multiple systems. Distributed componentscan operate sequentially or in parallel.

This written description uses examples to disclose the presentdisclosure, including the best mode, and also to enable any personskilled in the art to practice the disclosure, including making andusing any devices or systems and performing any incorporated methods.The patentable scope of the disclosure is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyinclude structural elements that do not differ from the literal languageof the claims, or if they include equivalent structural elements withinsubstantial differences from the literal languages of the claims.

Further aspects are provided by the subject matter of the followingclauses:

A decentralized power allocation system for an aircraft, comprising: apower bus; one or more electric power consumers electrically coupledwith the power bus; and a plurality of power source assemblies, each oneof the plurality of power source assemblies comprising: a power sourceelectrically coupled with the power bus; and a power controller forcontrolling electrical power provided from the power source to the powerbus, the power controller having power electronics and one or moreprocessors configured to: cause the power electronics to control a poweroutput of the power source to meet a power demand on the power busapplied by the one or more electric power consumers in accordance withan adaptive droop control scheme in which the power output of the powersource is controlled based at least in part on a correlation of a powerfeedback of the power source and a droop function that represents anefficiency of the power source to generate electrical power for a givenpower output of the power source.

The decentralized power allocation system of any preceding clause,wherein the droop functions associated with the power sources arecoordinated with one another so that the power output of a first powersource of the power sources is greater than the power output of a secondpower source of the power sources at power levels less than a referencepower level and so that the power output of the second power source isgreater than the power output of the first power source at power levelsgreater than the reference power level.

The decentralized power allocation system of any preceding clause,wherein, at a first power level that is less than the reference powerlevel, the power output of the first power source and the power outputof the second power source define a load share split of 100%/0% betweenthe first power source and the second power source to meet the powerdemand.

The decentralized power allocation system of any preceding clause,wherein, at a second power level that is less than the reference powerlevel but greater than the first power level, the power output of thefirst power source and the power output of the second power sourcedefine a load share split of 60%/40% between the first power source andthe second power source to meet the power demand.

The decentralized power allocation system of any preceding clause,wherein, at a third power level that is greater than the reference powerlevel, the power output of the first power source and the power outputof the second power source define a load share split of 40%/60% betweenthe first power source and the second power source to meet the powerdemand.

The decentralized power allocation system of any preceding clause,wherein, at a fourth power level that is greater than the referencepower level, the power output of the first power source and the poweroutput of the second power source define a load share split of 20%/80%between the first power source and the second power source to meet thepower demand.

The decentralized power allocation system of any preceding clause,wherein the droop functions associated with the power sources arecoordinated with one another so that the power output of the first powersource and the power output of the second power source are equal to oneanother at the reference power level.

The decentralized power allocation system of any preceding clause,wherein the power output of the first power source and the power outputof the second power source are equal to one another at the referencepower level so as to define a load share split of 50%/50% between thefirst power source and the second power source to meet the power demand.

The decentralized power allocation system of any preceding clause,wherein the first power source is a fuel cell assembly and the secondpower source is an electric machine.

The decentralized power allocation system of any preceding clause,wherein the electric machine is mechanically coupled with a gas turbineengine.

The decentralized power allocation system of any preceding clause,wherein the reference power level corresponds to a power level at whichthe droop function associated with the first power source intersectswith the droop function associated with the second power, and whereinthe power output of the first power source and the power output of thesecond power source are the same at the reference power level.

The decentralized power allocation system of any preceding clause,wherein the one or more processors of each of the power controllers isconfigured to: select the droop function from a plurality of droopfunctions based at least in part on one or more operating conditionsassociated with the aircraft.

The decentralized power allocation system of any preceding clause,wherein the one or more operating conditions include a flight phase.

The decentralized power allocation system of any preceding clause,wherein the one or more operating conditions include a health status ofthe power source and/or the power controller.

The decentralized power allocation system of any preceding clause,wherein the power bus is a direct current power bus.

The decentralized power allocation system of any preceding clause,wherein the droop functions are functions of voltage.

The decentralized power allocation system of any preceding clause,wherein the power bus is an alternating current power bus.

The decentralized power allocation system of any preceding clause,wherein the droop functions are active power droop functions that arefunctions of frequency.

The decentralized power allocation system of any preceding clause,wherein the droop functions are reactive power droop functions that arefunctions of voltage.

The decentralized power allocation system of any preceding clause,wherein the droop functions are linear functions having different slopesor wherein at least one of the droop functions is a non-linear function.

The decentralized power allocation system of any preceding clause,wherein the first droop function is a non-linear function and the seconddroop function is a linear or piecewise linear function.

The decentralized power allocation system of any preceding clause,wherein the first droop function is a curved, non-linear function andthe second droop function is a linear or piecewise linear function.

A method of operating a decentralized power allocation system for anaircraft, comprising: controlling a first power output of a first powersource to meet a power demand on a power bus applied by one or morepower consumers, the first power output being controlled based at leastin part on a correlation of a power feedback of the first power sourceand a first droop function that represents an efficiency of the firstpower source to generate electrical power for a given power output ofthe first power source; and controlling a second power output of asecond power source to meet the power demand on the power bus, thesecond power output being controlled based at least in part on acorrelation of a power feedback of the second power source and a seconddroop function that represents an efficiency of the second power sourceto generate electrical power for a given power output of the secondpower source, and wherein the first droop function and the second droopfunction are coordinated so that the first power output of the firstpower source is greater than the second power output of the second powersource at power levels less than a reference power level and so that thesecond power output of the second power source is greater than the firstpower output of the first power source at power levels greater than thereference power level.

The method of any preceding clause, wherein the first power source is afuel cell assembly and the second power source is an electric machinemechanically coupled with a gas turbine engine.

The method of any preceding clause, wherein the power bus is analternating current power bus, and wherein the reference power levelcorresponds to a point at which the first droop function and the seconddroop function intersect, wherein the first and second droop functionsare represented as functions of a frequency of the alternating currentpower bus versus power output of the first and second power sources.

The method of any preceding clause, wherein the power bus is a directcurrent power bus, and wherein the reference power level corresponds toa point at which the first droop function and the second droop functionintersect, wherein the first and second droop functions are representedas functions of a voltage of the direct current power bus versus poweroutput of the first and second power sources.

The method of any preceding clause, wherein the first power source is afirst fuel cell assembly and the second power source is a second fuelassembly.

A decentralized power allocation system for an aircraft, comprising: apower bus; one or more electric power consumers electrically coupledwith the power bus; a first power source assembly having a fuel cellelectrically coupled with the power bus and a first power controllerhaving first power electronics and one or more processors configured toexecute adaptive droop control logic so as to cause the first powerelectronics to control a power output of the fuel cell based at least inpart on a first droop function that represents an efficiency of the fuelcell to generate electrical power for a given power output of the fuelcell; and a second power source assembly having an electric machineelectrically coupled with the power bus and mechanically coupled with agas turbine engine, the second power source assembly also including asecond power controller having second power electronics and one or moreprocessors configured to execute adaptive droop control logic so as tocause the second power electronics to control a power output of theelectric machine based at least in part on a second droop function thatrepresents an efficiency of the electric machine to generate electricalpower for a given power output of the electric machine, and wherein thefirst droop function and the second droop function intersect at a pointcorresponding to a reference power level and are coordinated so that thepower output of the fuel cell is greater than the power output of theelectric machine at power levels less than the reference power level andso that the power output of the electric machine is greater than thepower output of the fuel cell at power levels greater than the referencepower level.

We claim:
 1. A decentralized power allocation system for an aircraft,comprising: a power bus; one or more electric power consumerselectrically coupled with the power bus; and a plurality of power sourceassemblies, each one of the plurality of power source assembliescomprising: a power source electrically coupled with the power bus; anda power controller for controlling electrical power provided from thepower source to the power bus, the power controller having powerelectronics and one or more processors configured to: cause the powerelectronics to control a power output of the power source to meet apower demand on the power bus applied by the one or more electric powerconsumers in accordance with an adaptive droop control scheme in whichthe power output of the power source is controlled based at least inpart on a correlation of a power feedback of the power source and adroop function that represents an efficiency of the power source togenerate electrical power for a given power output of the power source;wherein the droop functions associated with the power sources arecoordinated with one another so that the power output of a first powersource of the power sources is greater than the power output of a secondpower source of the power sources at power levels less than a referencepower level and so that the power output of the second power source isgreater than the power output of the first power source at power levelsgreater than the reference power level.
 2. The decentralized powerallocation system of claim 1, wherein the first power source is a fuelcell assembly and the second power source is an electric machine.
 3. Thedecentralized power allocation system of claim 2, wherein the electricmachine is mechanically coupled with a gas turbine engine.
 4. Thedecentralized power allocation system of claim 1, wherein the referencepower level corresponds to a power level at which the droop functionassociated with the first power source intersects with the droopfunction associated with the second power, and wherein the power outputof the first power source and the power output of the second powersource are the same at the reference power level.
 5. The decentralizedpower allocation system of claim 1, wherein the one or more processorsof each of the power controllers is configured to: select the droopfunction from a plurality of droop functions based at least in part onone or more operating conditions associated with the aircraft.
 6. Thedecentralized power allocation system of claim 5, wherein the one ormore operating conditions include a flight phase.
 7. The decentralizedpower allocation system of claim 5, wherein the one or more operatingconditions include a health status of the power source and/or the powercontroller.
 8. The decentralized power allocation system of claim 1,wherein the power bus is a direct current power bus.
 9. Thedecentralized power allocation system of claim 8, wherein the droopfunctions are functions of voltage.
 10. The decentralized powerallocation system of claim 1, wherein the power bus is an alternatingcurrent power bus.
 11. The decentralized power allocation system ofclaim 10, wherein the droop functions are active power droop functionsthat are functions of frequency.
 12. The decentralized power allocationsystem of claim 10, wherein the droop functions are reactive power droopfunctions that are functions of voltage.
 13. The decentralized powerallocation system of claim 1, wherein the droop functions are linearfunctions having different slopes or wherein at least one of the droopfunctions is a non-linear function.
 14. A method of operating adecentralized power allocation system for an aircraft, comprising:controlling a first power output of a first power source to meet a powerdemand on a power bus applied by one or more power consumers, the firstpower output being controlled based at least in part on a correlation ofa power feedback of the first power source and a first droop functionthat represents an efficiency of the first power source to generateelectrical power for a given power output of the first power source; andcontrolling a second power output of a second power source to meet thepower demand on the power bus, the second power output being controlledbased at least in part on a correlation of a power feedback of thesecond power source and a second droop function that represents anefficiency of the second power source to generate electrical power for agiven power output of the second power source, and wherein the firstdroop function and the second droop function are coordinated so that thefirst power output of the first power source is greater than the secondpower output of the second power source at power levels less than areference power level and so that the second power output of the secondpower source is greater than the first power output of the first powersource at power levels greater than the reference power level.
 15. Themethod of claim 14, wherein the first power source is a fuel cellassembly and the second power source is an electric machine mechanicallycoupled with a gas turbine engine.
 16. The method of claim 14, whereinthe power bus is an alternating current power bus, and wherein thereference power level corresponds to a point at which the first droopfunction and the second droop function intersect, wherein the first andsecond droop functions are represented as functions of a frequency ofthe alternating current power bus versus power output of the first andsecond power sources.
 17. The method of claim 14, wherein the power busis a direct current power bus, and wherein the reference power levelcorresponds to a point at which the first droop function and the seconddroop function intersect, wherein the first and second droop functionsare represented as functions of a voltage of the direct current powerbus versus power output of the first and second power sources.
 18. Themethod of claim 14, wherein the first power source is a first fuel cellassembly and the second power source is a second fuel assembly.
 19. Adecentralized power allocation system for an aircraft, comprising: apower bus; one or more electric power consumers electrically coupledwith the power bus; a first power source assembly having a fuel cellelectrically coupled with the power bus and a first power controllerhaving first power electronics and one or more processors configured toexecute adaptive droop control logic so as to cause the first powerelectronics to control a power output of the fuel cell based at least inpart on a first droop function that represents an efficiency of the fuelcell to generate electrical power for a given power output of the fuelcell; and a second power source assembly having an electric machineelectrically coupled with the power bus and mechanically coupled with agas turbine engine, the second power source assembly also including asecond power controller having second power electronics and one or moreprocessors configured to execute adaptive droop control logic so as tocause the second power electronics to control a power output of theelectric machine based at least in part on a second droop function thatrepresents an efficiency of the electric machine to generate electricalpower for a given power output of the electric machine, and wherein thefirst droop function and the second droop function intersect at a pointcorresponding to a reference power level and are coordinated so that thepower output of the fuel cell is greater than the power output of theelectric machine at power levels less than the reference power level andso that the power output of the electric machine is greater than thepower output of the fuel cell at power levels greater than the referencepower level.